This invention relates to a thermal head for use in a thermo-recording machine such as printer and facsimile and a method of manufacturing the same, and more particularly to a thermal head comprising a printing section including a wear-resistant layer having a printing surface to be brought into contact with a thermal record medium, a heat generating layer for generating heat to be transmitted to the thermal record medium through the wear-resistant layer and an electrically conductive layer connected to the heat generating layer, a driving circuit section connected to the electrically conductive layer of the printing section to control a heating electric power to be supplied to the printing section, and a wiring section for connecting the driving circuit section to an external circuit and a method of manufacturing such a thermal head.
A thermal head is an equipment, in which heat generated in accordance with a supplied electric signal is transmitted to a thermal record medium, for instance a thermal paper to record characters and figures of desired shapes. A conventional thermal head is composed of the following basic components:
(Component I) Printing Section
A printing section includes a printing surface to be brought into contact with a thermal paper and generates and transmits heat for coloring the thermal paper.
(Component II) Driving Circuit Section
A driving circuit section supplies an electric power according to an electric signal bearing information to be printed. Here, the information is to be understood to mean image data representing characters and figures. Since normal semiconductor integrated circuit chips are used as the driving circuit, the driving circuit is denoted as a driving IC for the sake of simplicity in the present specification.
(Component III) Wiring Section to External Circuit
A wiring section is provided for connecting the thermal head to a connector of a cable to be connected to an external circuit. The printing information and electric power are supplied to the thermal head from the external circuit via the wiring section. A connection to the external circuit is performed by a lead wire such as a flexible FPC (Flexible Print Circuit), and in this case, the wiring section includes pin-like conductors to be connected to the connector of the lead wire, a part of said pin-like conductors being exposed from the thermal head.
[Construction of Conventional Thermal Head]
Several examples of conventional thermal heads will be explained hereinbelow.
FIG. 1 is a cross sectional view showing a structure of an example of the conventional thermal head, in which a driving IC is connected to a printing section and a wiring section by means of wire-bonding. The thermal head shown in FIG. 1 has been used in a usual type thermo-recording printer. In FIG. 1, a reference numeral 10 denotes a wear-resistant layer having anti-physical and anti-chemical characters, a reference numeral 11 a heat generating layer, reference numerals 12a and 12b an electrically conductive layer constituting electrodes for the heat generating layer, a reference numeral 13 an electrically conductive layer constituting a wiring section for connecting the thermal head to an external circuit, a reference numeral 14 solders constituting connecting portions for connecting the wiring section and a wiring cable with each other, a reference numeral 15a driving IC, a reference numeral 16a wiring for connecting the driving to the external circuit, a reference numeral 17a heat storage layer, a reference numeral 18 a resin layer for isolating and protecting the driving IC and bonding wires, a reference numeral 19 an electrically insulating substrate, a reference numeral 20 bonding wires connecting terminals of the driving IC to the electrically conductive layer 12b and wiring section, a reference numeral 21 a thermal paper, and a reference numeral 22 represents a rubber roller for urging the thermal paper against the thermal head. A reference character P shows a printing section which is composed of a part of the wear-resistant layer 10, the heat generating layer 11 and parts of the electrically conductive layers 12a and 12b. A reference character S denotes the printing surface of the printing section P, that is a part of the surface of the wear-resistant layer 10 which is brought into contact with the thermal paper 21. A reference character L expresses a distance between the printing section P and the resin layer 18 protecting the driving IC 15.
In the known thermal head shown in FIG. 1, the heat storage layer 17 is formed on the substrate 19, on which the heat generating layer 11, electrically conductive layers 12a and 12b and wear-resistant layer 10 constituting the printing section P are successively stacked. The thermal head shown in FIG. 1 will be further explained by dividing it into several components.
(Component I) Printing Section
(Component II) Driving IC
(Component III) Wiring Section to External Circuit
(Component IV) Heat storage Layer
(Component V) Substrate
And particularly the printing section is constructed by stacking the following layers:
(I-1) Wear-resistant Layer
(I-2) Heat Generating Layer
(I-3) Electrically Conductive Layer
Therefore, the conventional thermal head illustrated in FIG. 1 is composed not only of the basic components (Component I), (Component II), and (Component III), but also by the heat storage layer of (Component IV). These components are arranged on the substrate 19 of (Component V). In other words, the (Component I)-(Component IV) are supported as a unit body by means of the (Component V).
The heat storage layer 17, however, is an additional component for attaining a power save. There are also proposed thermal heads, in which a heat radiating or other components for increasing a printing speed. By providing such a component, a performance of the thermal head can be improved. The heat generating layer II constituting the printing section P is divided into many heat generating elements in a direction normal to a plane of the drawing of FIG. 1. The electrically conductive layer 12a form a common electrodes to these heat generating elements and the electrically conductive layer 12b constitutes divided electrodes each being connected to respective heat generating elements in order to flow an electric current only through one or more desired heat generating elements according to the print information. The common electrode and divided electrodes are called the electrically conductive layer in a general term in this specification.
[Functions and Required Characteristics of Respective Components of Thermal Head]
Subsequently, functions of respective components will be explained.
At first, respective layers constituting the printing section P of (Component I) will be discussed.
(I-1) Wear-resistant Layer
The wear-resistant layer 10 is brought into contact with the thermal paper 21 to transmit the heat generated by the heat generating layer 11 to the thermal paper. Therefore the printing surface S is composed of the surface of the wear-resistant layer 10 situating in the printing section P. The wear-resistant layer 10 is required to have a basic characteristic that the layer does not chemically react to components contained in the thermal paper. Moreover good wear-resistant and heat-resistant characteristics, a lower coefficient of friction and a proper hardness are required for the wear-resistant layer. Furthermore, the wear-resistant layer preferably has a suitable electrical conductivity. This is due to a reason that dusts and charged particles might adhered to the printing surface S by an electrostatic charge caused by a friction between the printing surface and the thermal paper, said dust and particles causing a degradation in a print quality and undesired wear. Therefore, in order to prevent the charging, the wear-resistant layer preferably has a proper electric conductivity. However since an extended portion of the wear-resistant layer extending from the printing section P is brought into contact with respective electrodes of the electrically conductive layer 12b, the wear-resistant layer should have such a resistance that these electrodes are not short-circuited.
(I-2) Heat Generating Layer
The heat generating layer 11 has a function of generating heat for coloring the thermal paper. The principle of the heat generation is based on the Joule heat, wherein heat is generated by flowing an electric current through a resistive body. Accordingly the heat generating layer 11 is required to have a stable electric property around 400xc2x0 C. Here, the electric property mainly means a resistance and its change with time.
(I-3) Electrically Conductive Layer
The electrically conductive layers 12a and 12b are used to establish an electrical connection within the thermal head. The electrically conductive layer 12a constitutes the common electrode which commonly connects one ends of respective heat generating elements of the heat generating layer 11 to, for instance the ground potential point. The electrically conductive layer 12b constitutes many electrodes for connecting respective heat generating elements of the heat generating layer 11 to the driving IC 15 separately. To this end, bonding wires 20 are soldered to the electrically conductive layer 12b and driving IC 15.
Since the electrically conductive layers 12a and 12b are contacted with the heat generating layer 11, the electrically conductive layers are influenced by the heat of about 400xc2x0 C. generated during the printing operation. In a process of manufacturing the thermal head, the layers are heated to about 350xc2x0 C. during the formation of the wear-resistant layer 10. Consequently the conductive layers 12a and 12b are also required to have a stable electric property at around 400 C. Here, the electric property mainly means a resistance and its change with time.
The electrically conductive layer 13 constituting the wiring section is soldered to the driving IC 15 and bonding wires 20, and is also connected to wires, for instance the pins 16 by solders 14 for establishing a connection to the external circuit,
(Component IV) Heat storage Layer
The beat storage layer 17 has a function for holding the heat generated by the heat generating layer 11 for a certain time period and preventing the heat from being transmitted to the driving IC 15 through the resin layer 18. Thus the heat storage layer 17 should have a low thermal conductivity and a high heat-resistance.
(Component V) Substrate
The substrate 19 constitutes fundamentally a supporting body of the thermal head. That is to say, the substrate has a function for supporting the printing section P, driving IC 15, electrically conductive layer 13 constituting the wiring section for connecting the thermal head to the external circuit, wires 16 connected to the wiring section. The substrate may be heated to about 400xc2x0 C. during the manufacturing process. Thus the substrate 10 should have a high mechanical strength as well as a high heat-resistance. Moreover, the substrate preferably has a high thermal conductivity such that the heat generated by the thermal head during the printing operation could be dissipated.
Resin Layer 18
The resin layer 18 is used to protect the driving IC 15 and the bonding wire 20, and thus the resin layer should have a proper mechanical strength and a certain electrically insulating property.
[Substances of Respective Components of Thermal Head]
Now substances composing respective components of the thermal head, that is to say, respective layers of the printing section P and substrate 19 will be described. These components of the thermal head are made of substances which can satisfy the above mentioned characteristics.
Wear-resistant Layer
Although the wear-resistant layer 10 is preferably made of a substance which satisfies all the desired conditions mentioned above, such a substance could hardly be found. SiC based compound, SiB based compound, SiO based compound and SiON based compound may be listed as a substance which can satisfy the conditions to a relatively large extent.
Heat Generating Layer
The heat generating layer 11 has to be made of a substance which reveals a stable electric property at about 400xc2x0 C. The heat generating layer is made of a metal such as Ta, an alloy such as Nixe2x80x94Cr, a poly-Si and a mixture of a transition element and SiO2 such as Nbxe2x80x94SiO2. Among these substances, Nbxe2x80x94SiO2 has been generally used, because its resistance can be easily controlled.
Electrically Conductive Layer
The electrically conductive layer 12a, 12b and wiring section 13 should be made of a substance also having a stable electric property at about 400xc2x0 C. W, Ta, Au, Al and the like may be listed as such a substance.
In order to attain a desired resistance value and an easy connection to the driving IC 15, a multiple layer of the above stated metals may be used.
Heat Storage Layer
The heat storage layer 17 has to be made of a substance having a small thermal conductivity as well as a high heat-resistant property. Bakelite, polyimide, glass and the like may be listed as such a substance. The Bakelite is a trade name of phenol-formaldehyde. Glass has been generally used due to its hardness.
Substrate
The substrate 19 should be made of a substance having a high thermal conductivity and a high heat-resistance. MgO, ZnO, aluminum nitride, alumina ceramics and the like may be listed for such a substance. The alumina ceramics have been generally used due to its easy processing and low cost.
[Contact Between Printing Section and Thermal Paper]
Now a contact between the printing surface S of the printing section P and the thermal paper 21 during the printing operation will be explained.
The printing in the thermal head is carried out by conducting the heat generated by the heat generating layer 11 to the thermal paper 21 through the wear-resistant layer 10. Accordingly, in order to achieve a clear printing, the heat generated by the heat generating layer 11 has to be efficiently transmitted to the thermal paper 21, The more tight the contact between the printing surface S of the printing section P and the thermal paper 21 is, the better the heat transmission to the thermal paper 21 becomes. Therefore, the tight contact between the printing surface S of the printing section P and the thermal paper 21 has to be achieved by proper means. A method of making a tight contact between the printing surface S and the thermal paper 21 will be described while a facsimile is taken as an example.
In a machine in which the printing section P is arranged along a lateral line like as facsimile, the thermal paper 21 is generally urged against the printing surface S of the printing section P by means of the rubber roller 22. The rubber roller 22 also serves as a paper feeder. Accordingly upon designing the rubber roller 22, the hardness and shape of the rubber roller 22 are determined such that the tight contact can be attained between the printing surface S and the thermal paper 21 as far as possible.
[Connection of Driving IC]
Next, a method of establishing a connection to the driving IC 15 will be described with reference to FIGS. 2 and 3 in addition to FIG. 1. FIGS. 1-3 are cross sectional views showing the structure of known thermal heads. In the thermal heads depicted in FIGS. 2 and 3, the driving IC 15 is connected by means of the wire-bonding, and particularly the thermal head illustrated in FIG. 2 has the printing section which is higher than that of the thermal head shown in FIG. 1. In the thermal head illustrated in FIG. 3, the driving IC is connected by means of the flip chip bonding. Portions of the thermal heads shown in FIGS. 2 and 3 similar to those of FIG. 1 are denoted by the same reference numerals used in FIG. 1. It should be noted that in FIG. 2, a reference character I denotes a height from the surface of the substrate 19 to the printing section S, a reference character H a height from the surface of the substrate to a top of a bonding wire loop, and a reference character X represents a depressed portion of the printing section.
The driving IC 15 has been connected to the electrically conductive layer 12b and electrically conductive layers of the wiring section 13 by means of the following methods.
(Connecting Method 1) Wire Bonding
In the wire bonding method, a metal wire called a bonding wire is fused to the terminals of the driving IC as well as to an electrically conductive layer at a predetermined position. The wire bonding has been widely used as the connection method for the driving IC. The wire-bonding is described in, for instance Japanese Patent Application Publication No. 6-78004. FIGS. 1 and 2 show the driving IC 15 connected by a bonding wire 20.
(Connecting Method 2) Flip Chip Bonding
The flip chip bonding is a connecting method, in which solder balls are formed on a lower surface of the driving IC to be connected and the balls are fused to the conductive layer. The method is described in, for instance xe2x80x9cOki Electric Research and Developmentxe2x80x9d, No. 138, Vol. 55, No. 2. FIG. 3 illustrates the driving IC 15 connected by the flip chip bonding.
There has been further provided the following connecting method in addition to the above mentioned two methods.
(Connecting Method 3) TAB
TAB means Tape Automated Bonding. The tape is a connecting part formed by covering plural metal wires with an insulating resin and both ends of the metal wires are exposed on both ends. In the TAB method, the terminals of the driving IC are simultaneously connected to the electrically conductive layers at predetermined positions.
[Defect Caused by Wire Bonding]
As mentioned above, FIG. 1 shows the driving IC connected by the wire bonding. As can be understood from FIG. 1, when a distance between the driving IC 15 and the printing section P is small, the following defects might occur.
(1) As shown in FIG. 1, in the case that the driving IC 15 and the bonding wire 20 are covered with the protective resin 18, the resin might be brought into contact with the thermal paper 21 or rubber roller 22.
(2) On the other hand, in the case that the driving IC 15 and the bonding wire 20 are not covered with the protective resin 18, the driving IC and bonding wires might be brought into contact with the thermal paper 21 or rubber roller 22.
In each cases, there might be produced a problem that the bonding wires might be broken and adjacent electrically conductive layers might be short-circuited.
In order to solve such a problem, there may be considered the following two solutions.
[Solution for Avoiding Defect Caused by Wire Bonding and its Problem]
(Solution 1) A distance L Between the Driving IC and the Printing Section is Made Sufficiently Long
In this case, the distance L has to be at least about 10 mm, so that the thermal head could not be further miniaturized.
(Solution 2) A Height I of the Printing Surface S is Increased
In this case, the height I of the printing surface S measured from the surface of the substrate 19 has to be not less than 200 xcexcm. Now methods of making the height I of the printing surface S larger will be explained.
First as shown in FIG. 2, the heat storage layer 17 is formed on the substrate 19 such that its thickness is partially increased, and the printing surface S is formed on the heat storage layer such that the printing surface is protruded outwardly. Since the height H of a top of a loop of the bonding wires 20 is about 200 xcexcm, the above problem could not be solved as long as the height I of the printing section P is not less than 200 xcexcm. However, an actual height I of the printing surface S is about 50 xcexcm.
In practice, if the height I of the printing surface S is made not less than 200 xcexcm, surfaces of the heat generating layer 11 and electrically conductive layers 12a, 12b are also protruded outwardly, and therefore etching processes by a photolithography could not be performed accurately and a precision of pattern dimension might be decreased. Therefore, the electric characteristics are liable to fluctuate.
In the case of forming the heat storage layer 17 to have a partially hick portion, the depressed portion X is formed at a center of the printing surface S as shown in FIG. 2. Accordingly a tight contact could not be attained between the printing surface S and the thermal paper 21, and thus a print density might be reduced.
A solution for solving the problem of the depressed portion X in the printing section P is described in Japanese Patent Application Laid-open Publication No. 62-170361. In the solution, however, an addition process is required for forming a protruded portion on the heat storage layer 17 having a partially thickened portion, said protruded portion compensating the depressed portion X, and the process might become complicated and expensive.
(Solution for Mitigating Defect Caused by Wire Bonding]
The above mentioned (Solution 1) and (Solution 2) could not solve the problems of the undesired contact of the bonding wire 20 and resin 18 to the thermal paper 21 and rubber roller 22.
[Defect Caused by Flip Chip Bonding]
As explained above, in the example of FIG. 3, since the driving IC 15 is electrically connected by the flip chip bonding, after the driving IC is directly bonded to the conductive layer 12b and wiring section 13, the driving IC 15 is scaled with the resin 18. Therefore, the resin 18 might be brought into contact with the thermal paper 21 and rubber roller 22.
[Solution for Mitigating Defect caused by Flip Chip Bonding and its Problem]
In order to avoid the undesired contact of the resin 18 with the thermal paper 21 and rubber roller 22, the distance L between the driving IC and the printing section P has to be at least about 8 mm. Then, the thermal head could not be further miniaturized like as the above mentioned wire bonding.
Moreover a method of manufacturing the thermal head as shown in FIG. 4 is described in Japanese Patent Application Laid-open Publication No. 5-64905. In this method, a stainless steel plate is used as a provisional substrate 30 for manufacturing the thermal head as shown in FIG. 4 and after grinding the surface of the stainless steel plate as a mirror surface, a peeling-off layer 31 is formed by electroplating of copper, on which the wear-resistant layer 10, the heat generating layer 11, and the conductive layers 12a and 12b are deposited in turn as shown in FIGS. 4Bxcx9c4D and a heat storage layer 32 made of a heat-resist resin is formed as shown in FIG. 4E. Then, an alumina substrate 34 is adhered on the heat storage layer 32 with an adhesive 33 as shown in FIG. 4F, and thereafter the provisional substrate 30 is peeled off at the interface of the peeled-off layer 31 to expose the wear-resistant layer 10 as a printing surface. Moreover a part of the wear-resistant layer 10 remote from the printing surface is removed to expose a part of the conductive layer 12b, to which the driving IC is connected to complete the thermal head.
This conventional method of manufacturing the thermal head has the following problems.
(1) It is very difficult to grind the stainless steel plate constituting the provisional substrate 30 as a flat mirror surface.
(2) When a number of thermal heads are simultaneously manufactured, it is very difficult to peel off the substrate 30 mechanically, because a surface area of the substrate is large.
(3) A thickness and plating conditions of the Cu plating layer constituting the peeled-off layer 31 could not be easily managed.
(4) Since peeling-off process could not be applied to a thermal head in which the printing section is protruded like as a partial graze, the thermal head having such a protruded printing section could never be manufactured.
(5) Since a thermal conductivity of the provisional substrate 30 made of stainless steel is different from that of the printing section formed on this substrate, the printing section is liable to be deformed during manufacturing.
(6) Characteristics of the printing section are liable to be changed due to a stress which is produced upon peeling off the substrate 30 made of stainless steel and is applied to the printing section.
(7) Since the driving IC is arranged on a side of the printing surface of the wear-resistant layer like as the conventional thermal heads shown in FIGS. 1-3, the distance L between the printing section and the driving IC could not be shortened and the problems mentioned above with reference to FIGS. 1-3 are remained unsolved.
In the known thermal heads, the problems of undesired contact of the driving IC itself as well as of the electric connection parts of the driving IC to the thermal paper must be solved, the thermal head has to be large to a certain extent and the printing section has to be projected largely.
However, this solution results in the following difficulties.
(1) The thermal head could not be miniaturized, and therefore a high manufacturing efficiency and a low manufacturing cost could not be realized.
(2) Since the printing section of the thermal head could not be formed easily, it is difficult to further improve a printing quality.
(3) According to the known manufacturing method, in which after forming the printing section by depositing the films on the stainless steel substrate, the substrate is peeled-off, there are not only the problems in difficulty of manufacturing and in the deformation, but also the problem in variation of characteristics of the printing section.
Therefore, the present invention has for its object to provide a thermal head, in which although a size of the thermal head is made small, a driving IC and its electric connection parts are not brought into contact with a thermal paper and a rubber roller, and thus the electric equipment could be protected against the cutting-off and short-circuit and as a result of which, the manufacturing could be performed efficiently at a low-cost.
It is another object of the invention to provide a thermal head having a smooth printing surface which could attain a good contact with a thermal paper.
It is still another object of this invention to provide a method of manufacturing such a thermal head in an easy and less expensive manner without special processes and operations.
In order to attain the above objects, according to the invention, a thermal head comprises:
a printing section including a wear-resistant layer having a first surface constituting a printing face to be brought into contact with a thermal record medium and a second surface opposite to the first surface, a heat generating layer formed an a side of the second surface of the wear-resistant layer and generating heat to be transmitted to the thermal record medium through the wear-resistant layer, and an electrically conductive layer formed on a side of the second surface of the wear-resistant layer and connected electrically to the heat generating layer;
a driving circuit section connected to the electrically conductive layer of the printing section to control a heat generating electric power to be supplied to said printing section; and
a wiring section for connecting the driving circuit section to an external circuit;
wherein said driving circuit and wiring sections are arranged on a side of the second surface of the wear-resistant layer of the printing section.
In the thermal head according to the invention, since the driving circuit section and wiring section are arranged on a side of the wear-resistant layer opposite to the side which is to be brought into contact with a thermal record medium the driving circuit section and connecting wires could not be brought into contact with the thermal record medium and rubber roller, and therefore a distance between the printing section and the driving circuit section can be shortened and the thermal head can be miniaturized.
Upon practicing the thermal head according to the invention, the thermal head can be classified into the following four groups in accordance with its principal structure.
According to the first principal structure of the thermal head according to the invention;
said wear-resistant layer in the printing section has an extended part which extends beyond the printing section,
said electrically conductive layer has an extended part which extends on a side of the second surface of the wear-resistant layer,
said wiring section is provided on a side of the second surface of the extended part of the wear-resistant layer, and
said driving circuit part is composed of integrated circuit chips, terminals of which are connected electrically to the extended part of the electrically conductive layer and to the wiring section.
In the second principal structure of the thermal head according to the invention, the thermal head comprises a supporting member provided on a side of the second surface of the wear-resistant layer of the printing section for supporting the printing section, driving circuit section, and wiring section.
Said supporting member comprises a resin member for bonding and fixing the printing section, driving circuit section and wiring section integrally, said resin member may be preferably made of epoxy resin, acrylic resin, or silicone resin.
In the third principal structure according to the invention, said supporting member comprises a heat dissipating member and an adhesive layer for fixing at least said printing section to said heat dissipating member.
According to the fourth principal structure of the thermal head according to the invention, said supporting member comprises a flat plate and an adhesive layer for fixing at least said printing section to the flat plate.
In each of the above mentioned first to fourth principal structures of the thermal head according to the invention, said printing surface may be flat or may be protruded outwardly,
In the above explained third and fourth principal structures, said adhesive is preferably made of a resin selected from the group of epoxy resin, acrylic resin and silicone resin. Furthermore, said adhesive resin may contain powders such as alumina powders for increasing a thermal conductivity. Moreover, in the third and fourth principal structures, said means for fixing the driving circuit section and a part of the wiring section to said heat dissipating layer or flat plate may be preferably formed in the supporting member. This fixing member may be advantageously formed by a both-sided adhesive tape.
Moreover, in the third and fourth principal structures of the thermal head according to the invention, said adhesive layer is preferably made of thermosetting adhesive agent, heat-resistant inorganic adhesive agent or viscoelastic rubber.
In the thermal head according to the invention, said printing section is constructed by stacking the wear-resistant layer, heat generating layer and electrically conductive layer or by stacking the wear-resistant layer, electrically conductive layer and heat generating layer in this order viewed from the printing surface.
Furthermore, said printing section may comprise a protection layer on a side of the heat generating layer opposite to the printing surface, said protection layer preventing a diffusion of impurities into the beat generating layer. Said protection layer may be preferably made of at least one of SiNx and SiNx or a mixture thereof. In the thermal head according to the invention, said printing section may include a beat storage layer thermally coupled with the heat generating layer through the protection layer. Said heat storage layer may contain at least one of polyimide and glass. Particularly, the heat storage layer may be preferably made of a polyimide containing powders for adjusting its thermal conductivity.
The thermal head according to the invention may further comprises a heat dissipating body thermally coupled with the heat storage layer on a side opposite to the printing surface. Said heat dissipating body may be preferably made of at least one of Al, Cu, Ni, Fe, Mo and alumina ceramics.
In case of providing a heat dissipating member and flat plate, they may be preferably formed in such a shape that they are not directed contacted with the driving circuit section. Further, these heat dissipating body and flat plate may be preferably made of a material having a thermal conductivity not less than 6.27xc3x97104 J/mxc2x7hxc2x7xc2x0 C. like as the above mentioned heat dissipating body, and particularly they may be made of Al, Cu, Ni, Fe, Mo and alumina ceramics.
According to the invention, a method of manufacturing a thermal head including a printing section which includes a wear-resistant layer having a printing surface to be brought into contact with a thermal record medium, a heat generating layer which generates heat to be transmitted to the thermal record medium through the wear-resistant layer, and an electrically conductive layer connected to the heat generating layer; a driving circuit section connected to the electrically conductive layer in the printing section to control a heat generating electric power to be supplied to the printing section; and a wiring section which connects the driving circuit section to an external circuit, comprises:
a step of forming the printing section on a substrate such that the printing surface of the wear-resistant layer is opposed to a surface of the substrate and at least a part of the electrically conductive layer is exposed on a side remote from the substrate;
a step of forming the wiring section on a side of the wear-resistant layer in the printing section remote from the substrate and providing said driving circuit section on the wiring section as well as on an exposed surface of the electrically conductive layer; and
a step of separating said printing section, driving circuit section and wiring section from the substrate as an independent unit body.
In a preferable embodiment of the method of manufacturing the thermal head according to the invention, said wear-resistant layer is formed on the surface of the substrate to have an extended portion extending beyond the printing section, said electrically conductive layer is formed to have an extended portion beyond the printing section along said extended portion of the wear-resistant layer, and said driving circuit section is provided by connecting integrated circuit chips to the extended portion of the electrically conductive layer and to wiring section.
Furthermore, according to the invention, a recessed portion having a substantially semicircular cross sectional configuration is formed in the surface of the substrate and the wear-resistant layer of the printing section is formed along said recessed portion such that the printing surface to be brought into contact with the thermal record medium is formed to be outwardly projected, or said substrate has a flat surface and said wear-resistant layer is formed on this flat surface such that the printing surface to be brought into contact with the thermal record medium is formed to be flat.
In a preferable embodiment of the method of manufacturing the thermal head according to the invention, prior to separating said printing section, driving circuit section and wiring section from the substrate as an independent unit body, at least a part of the printing section, driving circuit section and wiring section is reinforced.
Such a reinforcing step may be carried out by adhering said printing section, driving circuit section and wiring section as a integral unit body or by adhering at least a part of the printing section, driving circuit section and wiring section to a supporting member or by adhering at least the printing section to a heat dissipating member with an adhesive layer or by adhering at least the printing section to a flat plate with an adhesive layer. In case of reinforcing with the adhesive layer, it is preferable to adhere at least said printing section to the supporting member, heat dissipating member or flat plate with a resin.
Furthermore, at least said printing section may be adhered to the supporting member, beat dissipating member or flat plate with thermosetting adhesive, silicone adhesive, heat-resistant inorganic adhesive or viscoelastic rubber.
Moreover, according to the invention, at least said printing section may be adhered to the supporting member, heat dissipating member or flat plate and at least a part of said driving circuit section and wiring section is secured to the supporting member, heat dissipating member or flat plate by means of a fixing member. This fixing member may be preferably formed by a both-sided adhesive tape. For instance, it is preferable to secure wires connected to the wiring section to the supporting member, heat dissipating member or flat plate by means of a both-sided adhesive tape and a common electrode connected to the electrically conductive layer constituting the common electrode may be secure to the supporting member, heat dissipating member or flat plate by means of a both-sided adhesive tape.